Skip to end of metadata
Go to start of metadata

You are viewing an old version of this page. View the current version.

Compare with Current View Page History

« Previous Version 5 Current »

About

These are two tasks carried forward from 1H2024 and some additional work identified in 2024

  1. Jivan has a small patch which detects generation of some redundant sign/zero extensions in the RISC-V backend.    This is not expected to produce any significant benchmark improvements, but mostly serves as a final catch for corner cases so that we don't have to debug them again.  To date cases detected have all been due to expansion of builtins which perform overflow checking of basic integer operations.
  2. Eliminate the redundant sign extension after an inlined strcmp.
  3. Eliminate the redundant sign extension after an inlined memcmp
  4. sCC code generation will often need mixed modes and would benefit from Jivan's trick
  5. Use Jivan's trick to expose the sign extended nature of SI/HI/QI mode return values.
  6. A signed comparison of a sign extended SI subreg against a constant with 0x8000000 clear can be turned into unsigned comparison in DImode
    1. This is a generalization of the min/max case that's currently handled in bitmanip.md.
    2. Investigate if we're already handling this (we may be), and if not explore the best way to fix
  7. Investigate Ajit's work (IBM) to exploit cases where masking can be viewed as zero-extension within REE
  8. In REE handle cases like (any_extend:DI (ashift:SI )) where the extension can be replaced by a SUBREG and then push the SUBREG into the operands generating word sized operations.  This helps code like this:



void foo(unsigned char *data, unsigned int lo_bit) {
  unsigned int mask = ((1UL << 1) - 1) << lo_bit;
  *data = (*data & ~mask) | ((1 << lo_bit) & mask);
}



One the unnecessary extension is eliminated a simple backend pattern can be used to simplify all that to a simple lb+bset+sb.

Stakeholders/Partners

RISE:

Ventana: Jeff Law

Rivos: Vineet (part time)

External:



Dependencies


Status

Development

IN PROGRESS


Development Timeline1H2024
Upstreaming

IN PROGRESS


Upstream Version

gcc-15

Spring 2025




Contacts

Jeff Law (Ventana)


Dependencies

None



Updates

  • Note that sCC expansion code can benefit from Jivan's trick as well.  Going through testing right now. 

 

  • Elimination of the redundant extension after inlined strcmp and memcmp are upstreamed.
  • Add note on comparisons

 

  • Add memcmp optimization to list
  • strcmp optimization submitted upstream

  • Breaking out additional items as 2H2024 work
  • No labels